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Documentation > Rule engine > Data processing & actions > Create and Clear Alarms
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Create and Clear Alarms

Use case

Let’s assume your device is using DHT22 sensor to collect and push temperature readings to ThingsBoard. DHT22 sensor is good for -40 to 80°C temperature readings. We want generate Alarms if temperature is out of good range.

In this tutorial we will configure ThingsBoard Rule Engine to

  • Create or Update existing Alarm if temperature > 80°C or temperature < -40°C
  • Clear Alarm if temperature > -40°C and < 80°C

Prerequisites

We assume you have completed the following guides and reviewed the articles listed below:

Adding the device

Add Device entity in ThingsBoard. Its name is Thermostat Home and its type is Thermostat.

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Message flow

In this section, we explain the purpose of each node in this tutorial:

  • Node A: Filter Script node.
    • This node with temperature threshold check script will verify: “if the temperature is in the expected interval, the script will return False, otherwise True will be returned”.
  • Node B: Create alarm node.
    • Creates or Updates an alarm if the published temperature is not at expected time range (filter script node returns True).
  • Node C: Clear alarm node.
    • Clears alarm if it exists in case if the published temperature is in expected time range (script node returns False).
  • Node D: Rule Chain node.
    • Forwards incoming Message to specified Rule Chain Create & Clear Alarms.


Configure Rule Chains

In this tutorial, we modified our Root Rule Chain and also created Rule Chain Create & Clear Alarms


The following screenshots show how the above Rule Chains should look like:

  • Create & Clear Alarms:

image

  • Root Rule Chain:

image


Download the attached json file for the Create & Clear Alarms rule chain. Create Node D as shown on the image above in the root rule chain to forward telemetry to the imported rule chain.

The following section shows you how to create this rule chain from scratch.

Create new Rule Chain (Create & Clear Alarms)

Go to Rule Chains -> Add new Rule Chain

Configuration:

  • Name : Create & Clear Alarms

image

New Rule Chain is created. Press Edit button and configure Chain.

Adding the required nodes

In this rule chain, you will create 3 nodes as it will be explained in the following sections:

Node A: Filter Script
  • Add the Filter Script node and connect it to the Input node with a relation type Success.
    This node will verify: “if the temperature is in the expected interval” using the following script:
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return msg.temperature < -40 || msg.temperature > 80;

If the temperature is in the expected interval the script will return False, otherwise True will be returned.

  • Enter the Name field as Under Threshold.

image

Node B: Create alarm

  • Add the Create alarm node and connect it to the Filter Script node with a relation type True.
    This node loads the latest Alarm with configured Alarm Type for Message Originator, namely Thermostat Home
    if the published temperature is not at expected range (filter script node returns True).

  • Enter the Name field as Create alarm and the Alarm type as Critical Temperature.

image

Node C: Clear Alarm

  • Add the Clear Alarm node and connect it to the Filter Script node with a relation type False.
    This node loads the latest Alarm with configured Alarm Type for Message Originator Thermostat Home
    and Clears alarm if it exists in case if the published temperature is in expected range (script node returns False).

  • Enter the Name field as Clear Alarm and the Alarm type as Critical Temperature.

image

Modify Root Rule Chain

The following screenshot shows the initial Root Rule Chain.

image

The initial Rule Chain has been modified by adding the following node:

Node D: Rule Chain

  • Add the Rule Chain node and connect it to the Filter Script node with a relation type True.
    This node forwards incoming Message to specified Rule Chain Create & Clear Alarms.

  • Enter the Name field as Create & Clear Alarms.

image


The following screenshot shows how the final Root Rule Chain should look like:

image



How to verify the Rule Chain and Post telemetry

For posting device telemetry we will use the Rest APIs, Telemetry upload APIs. For this we will need to copy device access token from the device Thermometer.

image

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**you need to replace $ACCESS_TOKEN with actual device token**

Let’s pushed debug mode button in Clear Alarm and Create Alarm node to verify the results.

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sent temperature = 99. Alarm should be created:

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curl -v -X POST -d '{"temperature":99}' http://localhost:8080/api/v1/$ACCESS_TOKEN/telemetry --header "Content-Type:application/json"

image

Lets post temperature = 180. Alarm should be updated:

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curl -v -X POST -d '{"temperature":180}' http://localhost:8080/api/v1/$ACCESS_TOKEN/telemetry --header "Content-Type:application/json"

image

Lets post temperature = 30. Alarm should be cleared:

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curl -v -X POST -d '{"temperature":30}' http://localhost:8080/api/v1/$ACCESS_TOKEN/telemetry --header "Content-Type:application/json"

image


Also, you can:

  • configure Alarm Details function in the Create and Clear Alarm nodes.

  • configure the Dashboard by adding an alarm widget to visualize the alarms.

  • define an additional logic for alarm processing, for example, sending an email.

Please refer to the links from the second to the fourth under the See Also section to see how to do this.


See Also

Next steps